High‐spin molecular rotation spectra are surprisingly simple

In the past few years enormous experimental and theoretical progress has been made toward the understanding of the vibration–rotation spectra of polyatomic molecules. With a laser spectrometer of unprecedented size and complexity, Christian Bordé and his colleagues at the Université Paris‐Nord are now able to resolve hyperfine and “superfine” splittings of less than one part in $1010$ over a considerable infrared wavelength range in the spectra of such molecules as sulfur hexafluoride. $SF6$ is particularly interesting not only because its highly symmetrical configuration produces astonishing spectral patterns that have given impetus to a new level of theoretical understanding; it also serves as a stand‐in for $UF6.$ Much of the support for $SF6$ spectroscopy has been impelled by the practical interest in laser separation of uranium isotopes.